This project involves the study of interactions between porphyrins and the tumor cell which, in the presence of light, lead to substantial selective toxicity. Appropriate porphyrins are localized in tumor tissues, but not in adjacent normal cells, so that the latter are spared from light-induced cell damage resulting from prophyrin-catalyzed production of singlet oxygen. Using fluorescence spectroscopy, we plan to monitor the drug-cell interactions which lead to selective localization of certain porphyrins in the tumor cell. Sites of such localization will be sought by comparison of fluorogenic interactions between cells and porphyrins with similar interactions in model membranes and reference solvents. Measurements of steady state fluorescence spectra, fluorescence lifetimes and polarization will be used to characterize sites of porphyrin binding.